This invention relates to ultra-violet (UV) stabilizers which are addition polymerizable and to polymers containing such stabilizers.
The demands made upon polymeric materials in industrial, commercial and consumer fields are continually increasing. To improve polymers, the use of UV stabilizers has been extremely important. UV radiation accelerates the physical and chemical deterioration of polymeric substrates and causes the fading of colors, the yellowing of cellulosics, the photo-oxidation of polyolefins, the dehydrochlorination of poly(vinylchloride), the imbrittlement of coatings, etc. UV stabilizers extend the useful life of irradiated polymers by absorbing UV radiation and/or absorbing the energy by intermolecular energy transfer and harmlessly dissipating the energy.
Three main factors affect UV stabilizer performance. The first is the intrinsic activity of the UV stabilization functional group. This may be evaluated by a number of conventional methods. The second factor is the compatibility or solubility of the stabilizer in the polymer system. This second factor is important in situations wherein a polymer may initially have a UV stabilizer dispersed throughout the system, however, upon aging the UV stabilizer may migrate from one polymer phase to another polymer phase or to the surface of the polymer. A third factor is the leaching or volatility of the UV stabilizer. This third factor, the leaching of the stabilizer, is very important in many situations. For many applications the UV stabilizer must be capable of withstanding multiple detergent washings and/or dry cleanings. In food or clothing related applications, the UV stabilizer must not be released so as to be absorbed by the body. In extraterrestial environments the UV stabilizers must have extremely low vapor pressures to remain in the polymer even at very high temperatures and very low pressures.
A number of approaches have been tried to solve the problem of the volatilization of UV stabilizers in polymeric materials. One such approach has been to chemically combine the UV stabilizer with the polymeric material sought to be protected. These attempts, however, have not been wholly satisfactory. The chemically combined stabilizers disclosed in the literature are generally expensive to manufacture in that they require synthesis routes which are energy intensive and time consuming. In addition, the products produced by these methods are often inadequate in their ability to function as a UV stabilizer. Further, the synthesis routes described in the literature generally produce large amounts of impurities which interfere with the UV stabilizer properties or other aspects of the polymer system in which they are employed. These routes also characteristically have low product yields.
Bailey et al., Polymeric Ultraviolet Absorbers, J. Macromol. Sci.--Rev. Macromol. Chem, C14 (2), pp. 267-293 (1976), and Kline, U.S. Pat. No. 3,953,402 (1976), discuss polymerizable UV absorbers made through an esterification reaction. These syntheses are energy intensive, and the products require considerable processing to obtain a relatively pure compound.
Coleman, U.S. Pat. No. 3,391,110 (1968), discloses a condensation polymer which has both a UV stabilizer moiety and a urethane linkage. There is no suggestion, however, of an addition polymerizable UV absorber.
Schroeter et al., U.S. Pat. No. 4,179,548 (1979), teaches a UV stabilizer which is useful in an addition polymer, but the UV stabilizer itself is not addition polymerizable. Further, although Schroeter et al. teach the reaction of a UV stabilizer with an isocyanate to form an urethane linkage, they do it for the purpose of temporarily disabling the UV stabilizer so that an UV radiation curing system may be used.
Accordingly, it would be desirable to have a polymerizable UV stabilizer which has high UV stabilization activity, is energy efficient to manufacture, may be quickly and easily manufactured, is relatively free of harmful impurities, and may be produced in high yield.